Method of producing steel cylinder barrels having bonded bronze valve plates

ABSTRACT

The disclosure concerns a process for providing the steel cylinder barrel of a piston pump or motor with an adherent, bronze valve plate. The finished valve plate is machined from a bronze member which is cast in place against one end of the cylinder barrel blank under conditions which effect a sound metallurgical and mechanical bond between the steel and the bronze.

United States Patent Alger, Jr. et a1.

[54] METHOD OF PRODUCING STEEL CYLINDER BARRELS HAVING BONDED BRONZEVALVE PLATES Martin J. Alger, Jr.; Nelson H. Dunn, both of Watertown,N.Y.

Assignee: General Signal Corporation Filed: Nov. 27 1970 Appl.No.:'93,129

Inventors:

References Cited UNITED STATES PATENTS 3 ,169,488 G allig e r u n gg/i'l1 Dec. 26, 1972 3,280,758 10/1966 Leeming ..91/499 853,716 5/1907 Monnot..164/1l2 2,066,247 12/1936 Brownback ..L ..164/8 0 2,207,150. 7/1940Hirsch et al. ..164/8O X Primary Examiner-.JohnF. Campbell AssistantExaminer- Donald C. Reiley lll Attorney-George Vande Sande, Harold S.Wynn & Jeffrey S. Mednick [57] ABSTRACT,

The disclosure concerns aprocess-forproviding the steel cylinder barrelof a piston pump. or motor with an adherent, bronze valve plate. Thefinished valve plate is machined from a bronze member which is cast inplace against one end of the cylinder barrel blank under conditionswhich effect a sound metallurgical and mechanical bond between the steeland the bronze.

' 8 Claims, 4 Drawing Figures METHOD OF PRODUCING STEEL CYLINDER BARRELSHAVING BONDED BRONZE VALVE PLATES BACKGROUND AND SUMMARY OF THEINVENTION In hydraulic pumps and motors of the rotary cylinder barrel,longitudinally reciprocating piston, type, oil usually is transferred toand from the cylinder bores through a rotary valve at one end of thecylinder barrel. This valve comprises a stationary element containingarcuate high and low pressure ports which subtend angles slightly lessthan 180, and an element which rotates with the cylinder barrel andcontains a circular series of small arcuate ports, each of whichcommunicates with one of the cylinder bores in the barrel. Since thevalving elements are in continuous sliding engagement with each otherduring operation, it is desirable, if not a practical necessity in thecase of high speed, high pressure hydraulic units, to make one of thetwo elements of bronze. This arrangement can be incorporated in severalways, but it is evident that the best approach for units which employsteel cylinder barrels is to use a bronze rotary valving element and tobond it directly to the end of the cylinder barrel. However, use of thisdesign has been limited by the lack ofa satisfactory process forproducing a bond between the steel and the bronze. v

The object of this invention is to provide a practical and reliableprocess for producing an adherent bronze valve plate on the valving endofa steel cylinder barrel. According to the invention, the new processis characterized initially by the formation of an assembly including asteel cylinder barrel blank, amold which receives the valving end of thebarrel and is shaped to define with an annular end face thereon a cavityin which a rough valve plate is to be cast, and a charge of bronze inthe solid state which is adapted to flow into and fill the cavity whenmelted. The assembly is heated in a non-oxidizing atmosphere to atemperature between l,900 and 2,000F to melt the bronze charge, effectfilling of the mold cavity, and to produce an intimate bond between thebronze and the steel end face of the cylinder barrel. Thereafter, theassembly is cooled in the controlled atmosphere to solidify the bronzeand then air cooled to room temperature/ Finally, the finished valveplate is machined from the rough cast bronze plate. This procedurecreates a true metallurgical, as well as a mechanical, bond between thebronze valve plate and the steel cylinder barrel, and the shape of themold cavity and the cooling rate of'the cast bronze member arecontrolled so that shrinkage, if any, occurs in a region of the castingwhich is subsequently machined away. The combined effect of thesefactors makes the process a practical and reliable production technique.

BRIEF DESCRIPTION OF THE DRAWING The preferred process is describedherein in detail with reference to the accompanying drawing in which:

FIG. 1 is an axial sectional view of the barrel blankmold-bronze chargeassembly as it appears prior to the heating cycle.

FIG. 2 is a sectional view taken on line 2-2 of FIG. 1.

FIG. 3 is an axial sectional view of the finished cylinder barrel.

FIG. 4 is a view of the valving face of the finished cylinder barrelshown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT The initial step of thepreferred process concerns formation of the assembly 11 (see FIG. 1)which includes a steel cylinder barrel blank 12, a mold 13 and a bronzecharge 14. Blank 12, which is rough machined from SAE 52100, 1045 or4l50 steel stock, hasa circular cross section, contains a through axialbore 15, and is provided with a flat annular end face 16 towhich thebronze valve plate is to be bonded. Face 16 is left in the rough turnedstate, since surface irregularities aid, rather than hinder, the bondingprocess. Moreover, it has been found that the process is not adverselyaffected by the formation of rust on fact 16. After machining, blank 12is cleaned to remove chips and then vapor degreased. Degreasing is notessential because any adherent oil or grease film will be burned offbefore the bronze-steel bond is effected. However, since these volatilesmay leave a residue on face 16 which could cause localized impairment ofthe bond, it is considered best to remove them initially.

Mold 13 is formed to receive the end ofblank 12 and to cooperate withface 16 to define a mold cavity 17. The outermost region of cavity 17 issubdivided by a circumferential series of uniformly spaced, radial ribs18 which define the dynamic bearing pads (see pads 19 in FIG. 4) of thefinished valve plate. Inboard of these ribs, the bottom wall 21 ofcavity 17 slopes downward toward the center so that the thickest portionof the bronze casting will lie adjacent the inner periphery of face16..This arrangement is important because it enables the central portionof the casting to act as a riser and concentrate shrinkage in a regionwhich is removed during final machining of the cylinder barrel. Becausemold 13 usually has a relatively large surface area and low masscompared to blank 12, it tendsto cool much more rapidly than the blank.This differential cooling can cause shrinkage in the region of thebronze-steel interface and adversely affect the bond. In order toprevent this, mold 13 is equipped with a heat-insulating jacket 22composed of a mass of asbestos fibers. Inclusion of the jacket tends toequalize the rates at which heat is transferred from the bronze throughblank 12 and through mold l3, and thus minimizes the risk of shrinkageat the bronze-steel interface. Mold 13 preferably is made of ceramicmaterial and carries a thin graphite coating 23 which serves as arelease agent for the casting, but carbon molds or graphite-coated steelmolds may be used. It also is possible to make the mold of core sand.However, this last alternative is not considered as reliable as theothers because, during the heating cycle, the binder in the sand gives.off gases which may accumulate in the empty cavity 17 and impair thebond which is to be created.

The bronze charge 14 is in the form of a cylindrical body which has anenlarged portion that fits within axial bore 15, and a smaller portionthat fits within a central-recess formed in mold 13. The charge,therefore, serves as a convenient means for centering blank 12 in themold during make-up of assembly 11. The

charge may be a solid bronze casting, but preferably is a sintered massof bronze powder because this form permits better control ofcomposition. While various bronzes may be used, experience indicatesthat the composition should be free of zinc and nickel because thesemetals tend to separate from the other constituen'ts and form a brittleinterface which may crack under the service conditions encountered bythe finished cylinder barrel. The composition should also have as low alead content as possible because this metal will bleed out" during heattreatment of the driving splines of the cylinder barrel. Bronzes havingthe following compositions, by weight, have proven acceptable: v

a. 80 percent copper, lOpercent tin, percent lead b. 89 percent copper,l 1 percent tin c. 90 percent copper, 10 percent tin However, thepreferred charge 14 is made of a bronze containing 85 percent copper, 10percent tin, and 5 lead, and which is purchased commercially in thenickel-free form.

It will be noted from FIG. 1 that the charge 14 is so positioned inassembly 11 that, when melted, the bronze will flow into mold cavity 17.The volume of metal in the charge is greater than the volume of thecavity so that the liquid level of the molten mass-will lie above theend face 16 of blank 12. This measure insures that cavity 17 will befilled completely and that the molten bronze will be in contact withface 16 throughout its whole area.

After assembly 11 has been completed, it is placed in a furnace andsupported therein in a level position, i.e., in a position which issufficiently level to guarantee that the liquidlevel of the moltenbronze will lie above face i l6 throughout'the full extent of thelatter. The furnace should contain a non-oxidizing atmosphere, suchasthe filtered natural'gas product commonly employed to controldecarburization of the steel in blank 12 during heat treatment. In atypical process, the furnace is at a temperature of about l,600F whenassembly is inserted, so the temperature must subsequently be raised toan elevated level above the melting range of the bronze and held therelong enough to insure that all parts of. assembly I] reach a temperaturewhich will produce a good metallurgicalbond between the bronze andsteel. Although bonding can be effected at an assembly temperature onthe order of l,900F, experience indicates that a temperature of 1,950Fis needed in order to provide the degree of bonding reliability requiredfor a production process. The furnace temperature and length of timethis temperature must be maintained in order to achieve the requiredassembly temperature must be determined empirically becausethese factorsvary with furnace design and loading, i.e., the number of assemblies 11being processed at the sametime. The final selection involves acompromise since higher temperatures shorten holding time but also causeexcessive evaporation of bronze and, because of localized hot spots,involve some risk of melting portions of steel blank 12. Our studiesshow that furnace temperatures above 2,000F are too risky and are notreally demanded by practical production considerations. For example,using a standard heat treating furnace capable of simultaneouslyprocessing thirty assemblies, we found that acceptable bonds wereproduced reliably at a furnace temperature of 1,990F which wasmaintained for one hour.

During the heating cycle just mentioned, charge 14 melts and the bronzeflows downward into mold cavity 17. Since the volume of bronze in thecharge is greater than the volume of the cavity, some of the moltenmetal will rise upward into bore 15 and around the outer periphery ofblank 1 2. In other words, the liquid level of the molten bronze masswill lie above the face 16 of blank 12. This is of vital importancebecause it insures that there will be contact between the bronze and thesteel over the entire area of face 16. As a result, a soundmetallurgical and mechanical bond will be effected over the entireinterface. A

At the end' of the heating cycle, i.e., after all parts of assembly 11have reached the selected bonding temperature, the furnace is allowed tocool so that the temperature of assembly reduces below the melting rangeof the bronze. Typically, this phase of the process consumes about 1hour, furnace temperature decreases to about 1,400F, and the temperatureof assembly 11 drops to a level below 1,500F. Theseconditions insuresolidification of the bronze and permit opening of the furnace withoutrisk of explosion of the controlled atmosphere. Assembly llis nowremoved from the furnace and allowed to air cool to room temperature.Dur- I ing these cooling phases of the process, some shrinkage may occurin the cast bronze valve plate blank; However, as mentioned above, theenlarged central mass of bronze and the insulation afforded by jacket 22to tend to confine this effect to the annular region adjacent the innerperiphery of face 16, which is removed during final machining.

After assembly 11 has cooled sufficiently to be handled, blank 12 isremoved from mold 13 and transformed into a completed cylinder barrel bythe final finishing operations. These include: v

l. Machining the inner and outer peripheral surfaces 24 and 25,respectively, and the front face 26.

2. Cutting and heat treating driving splines 27.

3. Drilling, boring and honing cylinder bores 28 and end milling arcuateports 29. I v

4. Machining bonded valve plate 31 to form land 32.

5. Grinding and lapping the faces of dynamic pads 19 and land 32.

Although the foregoing description treats only the process steps of thepresent invention, it should be un-' derstood that, in' the completecommercial process, bonding of the valve plate 31 is effectedsimultaneously with the cylinder liner bonding step of our applicationSer. No. 93,1 30, or Ser. No. 93,298, both filed concurrently herewith.

We claim: 1. A process for producing 'a bonded bronze valve plate on theend of a steel cylinder barrel for a pump or motor comprising the stepsof a. fabricating a steel barrel blank (12) having an end provided withan annular face (16); I

b. fabricating-a mold (l3) equipped with a surrounding heat sink (22)and formed to receive said end of the blank and define with said annularface a cavity (17) having a thickened cross section adjacent the innerperiphery of said face. 16);

c. preparing a mass (14) of bronze in the solid state which has a volumegreater than the volume of said cavity (17);

. heating said assembly (11) in a non-oxidizing at- I mosphere to atemperature between l,900 and 2,000F to thereby melt the bronze andcause it to fill said cavity (17) and form a metallurgical andmechanical bond with said annular face (16);

. cooling said assembly (11) in the presence of the non-oxidizingatmosphere to solidify the bronze in said cavity;

further cooling the assembly (11) to room temperature; and

machining the final valve plate (31) from the bonded bronze member and,in the course thereof, removing an annular region of bronze adjacent theinner periphery of said annular face.

the assembly (11) is cooled in the non-oxidizing atmosphere to atemperature between 1,400 and 1,500F; and

b. said further cooling is effected in air. 5. The process defined inclaim 1 in which a. the barrel blank (12) is made of SAE 52100, 1045 or4150 steel; and

b. the bronze mass (14) is a nickeLfree composition containing, byweight, percent copper, 10 percent tin, and 5 percent lead.

6. The process defined in claim 5 in which the bronze mass includes asintered slug of bronze powder.

7. The process defined in claim 1 in which a. the barrel blank (12) isformed with an axial bore (15) which is normal to and encircled by saidannular face (16); and

b. the mass (14) of bronze is in the form of a cylinder which fitswithin said bore and has an integral portion which fits a central recessin the mold (13),

c. whereby the bronze cylinder serves to center the blank with respectto the mold in said assembly.

8. The process defined in claim 7 in which a. the mold (13) is made ofceramic and is coated with a graphite release agent;

b. the barrel blank (12) is made of SAE 52100, 1045 or 4150 steel;

0. the bronze mass (14) is a nickel-free composition containing, byweight, 85 percent copper, 10 percent tin and 5 percent lead;

d. the assembly (11) is heated to a temperature of e. the assembly (11)is cooled in the non-oxidizing atmosphere to a temperature between l,400and 1,500F; and

f. said further cooling is effected in air.

2. The process defined in claim 1 in which the mold is made of ceramicand is coated with a graphite release agent.
 3. The process defined inclaim 1 in which said assembly (11) is heated to a temperature of1,950*F.
 4. The process defined in claim 1 in which a. the assembly (11)is cooled in the non-oxidizing atmosphere to a temperature between1,400* and 1,500*F; and b. said further cooling is effected in air. 5.The process defined in claim 1 in which a. the barrel blank (12) is madeof SAE 52100, 1045 or 4150 steel; and b. the bronze mass (14) is anickel-free composition containing, by weight, 85 percent copper, 10percent tin, and 5 percent leAd.
 6. The process defined in claim 5 inwhich the bronze mass includes a sintered slug of bronze powder.
 7. Theprocess defined in claim 1 in which a. the barrel blank (12) is formedwith an axial bore (15) which is normal to and encircled by said annularface (16); and b. the mass (14) of bronze is in the form of a cylinderwhich fits within said bore and has an integral portion which fits acentral recess in the mold (13), c. whereby the bronze cylinder servesto center the blank with respect to the mold in said assembly.
 8. Theprocess defined in claim 7 in which a. the mold (13) is made of ceramicand is coated with a graphite release agent; b. the barrel blank (12) ismade of SAE 52100, 1045 or 4150 steel; c. the bronze mass (14) is anickel-free composition containing, by weight, 85 percent copper, 10percent tin and 5 percent lead; d. the assembly (11) is heated to atemperature of 1,950*F; e. the assembly (11) is cooled in thenon-oxidizing atmosphere to a temperature between 1,400* and 1,500*F;and f. said further cooling is effected in air.